Contact printing apparatus

ABSTRACT

A diazo printer which makes copies of a transparent or translucent type original by automatically measuring the density of the original and thereby controlling the printing speed of the apparatus to produce an exact copy. A developer system is synchronized with the printing speed over a wide range of the latter so that any such type of original can be copied by the apparatus. The width of the copy, as well as the length thereof, match that of the original by a copy control circuit that also operates a supply roll feed mechanism of preselected width corresponding to the width of the original. A vertical cabinet houses the various parts of the apparatus so that they are easily accessible for serving and/or replacement.

United States Paten Berge et a1.

[54] CONTACT PRINTING APPARATUS [21] Appl. No.: 70,221

[52] US. Cl ..355/111, 355/29 [51] Int. Cl. ..G03b 27/10 [58] Field ofSearch....355/28, 29, 68, 104, 106, 108,

[56] References Cited UNITED STATES PATENTS 3,484,168 12/1969 Toby..355/106 3,507,573 4/1970 Sage et al. ..355/28 3,474,692 10/1969 Sames..355/29 UX 2,918,857 12/1959 Frantz ..355/107 [15] 3,684,373 Aug.15,1972

FOREIGN PATENTS OR APPLICATIONS 75,654 8/1954 Netherlands ..355/108Primary Examiner-Samuel S. Matthews Assistant ExaminerFred L. BraunAtt0meyWalter C. Kehm, Samson B. Leavitt and Martin Smolowitz 5 7ABSTRACT A diazo printer which makes copies of a transparent ortranslucent type original by automatically measuring the density of theoriginal and thereby controlling the printing speed of the apparatus toproduce an exact copy. A developer system is synchronized with theprinting speed over a wide range of the latter so that any such type oforiginal can be copied by the apparatus. The width of the copy, as wellas the length thereof, match that of the original by a copy controlcircuit that also operates a supply roll feed mechanism of preselectedwidth corresponding to the width of the original. A vertical cabinethouses the various parts of the apparatus so that they are easilyaccessible for serving and/or replacement.

2 Claims, 6 Drawing Figures PATENTEDAUG 15 I972 SHEET 2 0F 5 Fig. IA.

INVENTORS Rm? 'i. (bege R 9.. NW 0 le SD PATENTEDAUB '15 um SHEET 3 [If5 Rat-9 4.. 'SQMs 0- Lnk YowG PAlENTEnAuslsmz 3,684,373 sum u 0F 5 INVENTORS E1. 0mm

CONTACT PRINTING APPARATUS This invention relates to photo-copiers, andmore particularly to diazo printing apparatus.

While the art of making diazo prints is known, there presently exists apressing need for more compact, efficient and effective apparatus tomake clear diazo prints automatically from any type of transparent ortranslucent original over a range of widths and lengths thereof.

The main object of this invention is to satisfy such need by theprovision of a novel machine for making diazo prints quickly,economically and automatically, which prints are exact and faithfulcopies of the corresponding originals both in size and appearance.

Another object is to provide a novel and convenient upright cabinet inwhich the various elements of the apparatus are housed, whereby theparts are readily available for servicing, and in which the operationsoccur in upwardly moving sequence with respect to an original feedingtable that is about waist high, with the original and copy output trayslocated within a central alcove above such table, between hollow sidewalls having instrument and control panels at the front thereof.

A further object is to provide means for automatically sensing therelative density of each moving original, and thereby continuouslycontrolling the relative speed of the copying operation to produce anexact copy.

A still further object is to provide means for automatically sensing thewidth and length of each original, and thereby selecting one of aplurality of copy supply rolls corresponding to such width, which isthen used to supply the copy that is cut to the corresponding length ofthe original.

Other objects are to improve the quality of diazo copies with anautomatic machine that is simple to construct and operate, even byunskilled personnel.

Briefly, the invention provides an upright cabinet in which the variousparts of the apparatus are housed. About waist high, the cabinet has ahorizontal original in slot. In front of such slot an original feedingtable is mounted which extends forwardly of the cabinet. Above suchtable are hollow side walls having front control panels provided withknobs and instruments associated with the control circuit of theapparatus in the cabinet. An original return or out station, and a copyoutput tray are located in an alcove between the side walls of thecabinet above the original table.

In the lower part of the cabinet are a plurality of copy supply rolls ofdifferent web widths for selective operation depending upon the width ofthe original that is fed into the in" slot. An inclined way for suchoriginal extends from such slot toward the interior of the cabinet, andbelow such way is a copy web cutter which is operated automatically tocut the copy so that it exactly matches that of the original.

The original and corresponding copy then merge and pass around a lightexposure station, upwardly through a separator and then the copy movesthrough a developing system. The original is split from the copy in suchseparator and is normally discharged onto the original out station,while the copy moves upwardly above such system. Means are provided forselectively discharging the finished copy into a front tray, or a reartray; while additional means are provided for discharging copies withtheir originals before such copies enter the developing system, ifdesired.

The present machine is provided with novel means for achieving a veryhigh degree of accuracy of cutting and exact registration of each copywith the corresponding original. Also, a unique feature is provided inthat, when the end of a copy paper roll is reached, any remainingremnant is caused either to pass harmlessly through the machine, or canbe easily retrieved by the operator. In addition, in order to avoid thecutting of undesirable slivers when drawn from alternate rolls, the edgeof the copy paper awaiting feeding through the knife, is moved slightlyback from the knife edge subsequently to each cutting operation.

In addition, the invention provides means for continuously controllingthe relative speed of printing in accordance with the relative densityof the original, as the latter advances toward a line of merger with thecorresponding copy paper prior to exposure thereof with such original,whereby clear copies are obtained. Such means utilizes light from theexposure source to pass through each moving original onto a photo-cellwhich measures the density of the original, and thereby operates acontrol circuit which varies the drive speed of the overlapping originaland copy paper elements as they move throughthe exposure area, through amotor that drives belt means carrying such elements.

In the drawings: I

FIG. 1 is a fragmentary perspective view of a diazo printing machineillustrative of the invention.

FIG. 1A is an enlarged fragmentary exploded view of the lower parts ofthe machine shown in FIG. 1.

FIG. 2 is an enlarged fragmentary perspective view of the console shownin FIG. 1, detailing the original movement sensors.

FIG. 3 is a fragmentary perspective view of the copy developer system.

FIG. 4 is a circuit diagram of the paper web feed cutter control system.

FIG. 5 is a circuit diagram of the original density/printing speedcontrol system.

Referring to FIG. 1, the diazo printer illustrated is housed within anupright cabinet 10 having a waist-high original feedboard or table 12.Located directly above the inner edge of the table 12 is an originalin-feed" slot 14 leading to an inclined original way 16 formed by spacedguide sheets 18,18 and an infeed roller system 20 provided with aphoto-cell density sensing system 22. Printer belts 24, located behindthe way 16 carry the original and copy in overlapped relationshipupwardly around a transparent printer cylinder 26 containing anelongated high-intensity central lamp 28 and a reflector 30. The ends ofthe lamp 28 and reflector 30 are mounted on end members which are, inturn, removably attached to the side walls 32 of the cabinet. Thecylinder 26 rolls with the belts 24, original, and copy, on thrustbearings 34 and 36.

Located in the cabinet under the inclined way 16 is a multi-copy-widthpaper supply roll compartment 38 having an access door 40 in the frontunder the table 12. Copy paper supply rolls 42 and 44 having mandrels 43and 45 are mounted in the compartment 38 on inclined end guide rails 46and 48, respectively. The mandrels are held in place adjacent the innerends of the guide rails 46 and 48 by locking levers 50 and 52,respectively. Copy paper 54 and 56 from the rolls 42 and 44 are threadedinto a lower set 58, and an upper set 60, respectively of infeed rolls.Such roll sets 58 and between upper and lower guide sheets 74 and 76which direct the web to printer infeed drive roller 78. r The papersupply roll compartment 38 is made lighttight and ammonia-vapor proof bymeans including an angular rear partition 80 which extends upwardly,

backwardly and then upwardly again from'the floor of the cabinet to apoint near the roller 78. Other printer-belt support rollers 82, 84 and86 maintain a closed loop of belt 24 about the printing cylinder 26 andprint separator section 87. The print and original are separated at 88.Adjacent to and directly in front of the print separator section 87 is atracing (original) separator 89 comprising an elongated separator tank90 which is surrounded by transport belts 92, driven by a roller 94, andguided by a dancer roller 96 onto a removable tray 98. The tray 98 isremovably mounted in an upper front space or alcove 100 formed betweenhollow side walls 102 of the cabinet 10 above the table 12, providing alarge original stacking area for extra large or roll drawings at theoption of the operator.

A print return lever 104 comprises means for setting pick-ofi fingers106 to cause both copy and original to be discharged onto the stackingarea when desired. Above the fingers 106 is a re-feed station 108containing a guide 110 for directing the copy to a developer tank 112.Within tank 112 are housed print in-feed rol lers 114, paper guide'wires116, ammonia drip tube 118, heater rods 120, and print feed-out rollers122.

Front delivery rollers 124, or rear delivery guide rollers 126,controlled by a print delivery selection lever 128, determines whetherthe finished print is delivered into a front tray 130, or into a reartray 132. The tray 130 is mounted in the space or alcove 100, betweenthe hollow side walls 102 of the cabinet 10, above the original out"tray 98. The rear tray 132 is located within the upper back area 134 ofthe cabinet 10.

The ammonia circulating system also includes a blower 136 associatedwith tank 112 for recirculating ammonia vapors therein and therebyimparting ammonia fumes directly on the prints to assume high qualitycopies. Heat and unwanted fumes tending to accumulate within the rear ofthe cabinet 10 are exhausted by a cooling and blower system 136 locatedbehind the partition 80. The entire machine is movable from one floorlocation to another on castors 138, and can be set in such position byadjusting leveling jacks 140 located adjacent the lower corners underthe cabinet 10.

Referring to FIG. 1A, as well as FIG. 1 after the paper rolls 42 and 44are loaded in place and locked in such position, the leading ends ofeach web are threaded under tiltable cutting blades 142 and 144, and onrollers 146 and 148, respectively. Each web is then gently torn acrossthe corresponding blade 142, 144 to provide a straight edge remainingthereon for subsequent transport through the machine. Jog switch 150then is operated to advance the lower web, and jog switch 152, toadvance the upper web, while light pressure is maintained on theappropriate cutter blade 142,

144, until the webs reach the printer cylinder, At such point, in eachcase, the jog switch 150, 152 is released and a manual cut switch 154 isactuated, resulting in a clean cut with the unwanted pieces of copypaper passing through the machine. The paper passing through the rollsets 58 and 60, respectively, is normally slack, fonning an elevatedloop 156, 158 between rolls 160 and 162 in one case,- and between rolls164 and 166 in the other case. The web loop 156, or 158 in each case,thus, is caused to bear or ride against a-sensing switch arm 168 or 170which operates looprollers 160, 162 or 164, to draw paper from supplyroll 42 or 44. Metering rolls 172, I74 drive the paper from the loop sothat the web is at substantially zero tension. The loop rollers 162, 164draw the paper from the supply rolls 42, 44, and are controlled byswitch arms 168, 170, so that when the loops 156, 158 recede, looprollers 162, 164 operate and replenish the loops 156, 158. v

The original to be copied is placed on the table or feedboard l2 and thefront edge gently inserted into the infeed roller system comprisingbrush rollers 172 and lower guide sheet 18 constituting in slot 14,thence toward its destination by three sets of transport rollers 20 inthe inclined way 16. As the leading edge of the original passes over asensing switch 171, FIG. 2, a brake 184, FIG. 1A, and the roll-feed isde-energized. As the leading edge of the original subsequently passesover a sensing switch 173, FIG. 2, which energizes one of the meteringrolls 172 or 174, which drives the selected copy paper web toward itsdestination. Loop rollers 160, 164 then function as previouslydescribed, the loops 156, 158 being alternately formed and reformedunder the corresponding switch arms 168, 170. 1

The original and copy paper converge simultaneously back of V-shapedguide 176 before passing between conveyor belt 24 on roller 78 andrubber rollers 178. The trailing edge of the original eventually passesover sensing switch 180, FIG. 2, which'thereupon de-energizes meteringclutch 182, thereby disengaging the related metering roller 172, 174.This results in the energization of a brake which stops the meteringroll, and energizes knifesolenoid 186. Thus the copy paper is cutquickly and efficiently by the cutter 70, FIG. 1A.

Printer belts 24 transport the original and copy paper behind theprinting cylinder 26 and reflector 30, FIG. .1, where exposure to thehigh intensity lamp 28 occurs. Subsequent to such exposure, the originalis separated from the copy by separator tank 90 and transport belts 92,under rollers 96, and advances thereby onto the receiving tray 98 whereit is neatly stacked. The separator tank 90 enhances such separation bycausing the copy to adhere to the printer belts 24 which deliver suchcopy upwardly to the ammonia vapor-filled developer tank 112, FIG. 1,between the lower seal and transport rolls 1 14, 114 in such tank.

Referring to FIG. 3, the copy is guided through the developer tank 112by pick-ofi shoes 188, 188, wire guides 116, between outfeed rollers122, 122, and pickoff shoes 190, 190. The copy then moves out of tank112, the front delivery roll 124 and under the rollers 192 via guide194, FIG. 1, and onto the front delivery tray 130. The resulting printsare dry, of thigh quality,

and neatly stack on the tray tray 130. Adjustment of the print deliveryselector lever 128, FIG. 1, can be made to reposition the guide todirect the copy through the rear delivery rollers 126 and 196 onto therear delivery tray 132, if desired,

The developer tank 112, FIG. 3, contains a plurality of heater elements118, and isprovided with a thermoswitch 198, as well as with thecross-flow blower 136, which recirculates the ammonia fumes forhomogeneous effect, as well as impacts fumes through longitudinalnozzles 200 onto copy moving through the guide wires 116.

Accurate registration of the copy with the original, as well as accuratecutting of the copy to match its original is obtained as follows:Referring to FIG. 2, a machine speed sensor 202 provides compensationfor the response time of the metering clutch 182, FIG. 1A, and knifesolenoid 186 over the entire range of machine speeds. Sensing switch180, FIG. 2, is mounted on a movable bracket 204 which is coupled to thespeed sensor 202 by flexible cords 206 and 208. The switch 173 ismounted on movable bracket 209 which is coupled to the speed sensor 202by flexible cords 208 and 210. Switch 173 is the copy paper feed switchand-controls the operation of metering clutch 182, FIG. 1A, and therotation of metering roller 174. The cut off switch 180, FIG. 2,controls actuation of brake 184, FIG. 1A, and actuation of the knifesolenoid 186. As the machine speed increases, speed sensor 202 displacesswitch 173 and switch 180 in proportion to the speed, resulting in anearlier signal to the metering clutch 182, FIG. 1A, to feed copy paper.At the same time, an earlier signal goes to the knife solenoid 186, FIG.1A, to cut the copy paper.

Conversely, as the machine speed decreases, switch 173, FIG. 2, andswitch 180 are effectively displaced to provide a later signal to themetering clutch 182, FIG. 1A, and to the knife solenoid 186. Appropriateadjustments result in very accurate cutting of the copy paper to theexact size of the corresponding original, as well as accurateregistration of the image on such copy paper.

In normal operation, sensing switch 171, FIG. 2, deenergizing brake 184,FIG. 1A, is activated before the sensing switch 173, FIG. 1A, isactivated, to actuate the metering clutch 182. This allows for brakedrop-out time, but results in possible creep of the metering roller 174and copy paper, due to such time lapse. Such copy paper creep, ifpermitted, results in inaccuracy of the copy paper size. This isovercome by a mechanical dampening brake 212 comprising a friction disc214, spring 216, and collar 218 on the loop :roller 174; and adjacent toretaining collar 218 on the loop roller 148.

The brake 212 also serves to stabilize loop roller 148, eliminatingoscillation normally caused by the weight of the copy paper hanging downfrom roller 148. If not dampened, the weight of such paper would resultin roller 148 free-wheeling in reverse, and the loop 158 receding,starting the cycle of switch arm 170 for replenishing the paper.Continuous drag braking of the paper supply rolls 44 is accomplishedthrough friction applied by a brake arm 214 on a drum 216 attached tothe mandrel 45; a similar arrangement brakes the roll 42.

Switch arm 168 which controls the loop 158, also serves as anend-of-roll detector. When the paper roll 44 is depleted, arm 168 dropsinto an opening 218 in paper guide 222, triggering a micro-switch (notshown) which operates a reload light 224, FIG. 2, de-energizing loopclutch 226, FIG. 1A, metering clutch 182, and knife solenoid 186, whilethe brake 184 is given a short (4 miIli-second) pulse on. Such brake on"pulse stops the copy paper remnant, allowing for easy retrieval if theleading edge had not-reached printer belt drive roller 78; or allowingthe remnant to pass through the machine, provided the leading edge hadreached the roller 78. Either condition allows the original to follow anormal course through the machine undamaged.

A problem associated with drawing copy paper from alternate rolls in atwo roll machine is a slight overhang of the copy paper at thestationary cutter or knife 68, resulting in the cutting of such overhangwhen the alternate paper is cut.

This produces an unwanted sliver of paper which falls somewhere in thecutting station 66 in the paper path. Such problem is solved by thefollowing novel innovation: The trailing edge of the copy paperenergizes, through sensing switch 180, FIG. 2, the brake 184, FIG. 1Aand knife solenoid 186. Metering clutch 182 was previously deenergizedby the sensing switch 171, FIG. 2. The armature 229 of brake 184, FIG.1A, is affixed to and rotates with the copy paper metering roller 174,while the coil 231 of brake 184 floats on the paper metering roller 174.But the amount of brake coil rotation is restrained by an arm extension228 between fixed posts 230. The slight rotation of the brake coil 231occurs when the brake armature 229 engages the brake coil 231. The brakeresponse time is about 3-5 milliseconds, while the knife solenoidresponse time is about 21 milIi-seconds. When sensing switch 180 signalsbrake 184 to energize, the brake coil 231 and armature 229 rotateclockwise, due to the pull of copy paper by the belts 24 in thedirection of paper travel. Such rotation islimited only by arm 228engaging a post 230, and occurs when the brake 184 responds to the sameoriginal. As the knife 70 cuts copy paper, brake 184 on metering roll174 is rotated counterclockwise to the extent allowable by arm 228 andpost 230 against the bias of a tension spring 232.

Referring to FIG. 2, a manually operable paper selector switch knob 234is provided for setting the width of the copy paper. Such knob 234 whenset for Automatic" results in the control circuit making such selectionas required by the width of the original. In such case, when a wideoriginal is fed into the machine, it actuates wide roll selector switch236, whereas when a narrow original is fed into the machine it missesthe switch 236. Locating paper roll selector 234 at either upper" orlower" allows selection of copy paper from either one, regardless of thewidth of the original. Such positioning also allows depletion of aselected roll by by-passing through appropriate circuitry either sensingarm 168, or 170, FIG. 1A, which normally would disable metering clutch182 and knife solenoid 186 when the end of the paper roll is reached.

The cutter members 68 and 70 at the cutting station 66 are in the formof a self-locating module that is easily removable from the, cabinet 10for servicing and/or replacement.

Referring to FIG. 4, the illustrated roll feed control circuit providesaccurate registration of diazo prints to the master over a wide range oftransport speed. This is accomplished by sensing the paper edges withthe mechanical switches 171, 173 and 180. Accuracy, freedom fromcontact-bounce uncertainty, is achieved by starting time-criticalfunctions on contact opening. Closed contacts of switch 171, forexample, short the bases of two transistor switches 306 and 303 tocircuit ground G. When the switch contacts open, the base shunt isremoved and the supply resistor current turns on the clutch or braketransistor. The inductive components of the brakes and clutches are 12voltunits. They draw 0.6 amp when on. During an OFF period, the suppliesfor the in-use clutch and either brake have a 500 mfd capacitor 236which is charged to 42 volts to speed the current build-up and actuationof such inductive components.

Power for the knife solenoid 186 is stored in a large (9K to 15K MFD)capacitor 238 charged to 42 volts. It delivers impulses of about 14joules (watt-seconds), and it recharges in less than one second forsucceeding shots.

The brake transistor triggers a 37 ms single shot which turns on the Q1power transistor 238 if the emitter of Q10 transistor 240 is grounded bythe enable circuit.

One of the two rolls of diazo paper is fed and cut to duplicate themaster transparency. Inputs come from the following three paper senseswitches:

I Brake-off and clutch-off switch 171.

2. Brake-on and Cut-on-trailing-edge switch 180.

3. Clutch-on, for leading edge switch 173.

Switches 180 and 173 are moved by thespeed governor, forward in time asthe transport speed increases. Switch 173 moves a smaller distance tocompensate for the clutch lag (about 3 ms) and the variable accelerams)knife lag. The knife cut occurs in about 4 ms at the end of this period.

Additional inputs are:

Enable the normally open contact of the No. 3 master sense switch 173enables an automatic knife actuate only while paper is still depressingthis switch. This prevents knife cuts which would be caused by contactbounce while the leading edge is taking the brake off at No. 1 8L No. 2switches 170 and 180.

Manual Cut A two pole switch 154 closes the enable circuit and deliversa pulse to the knife pulse timer, a 37 ms. single shot.

Manual Roll Select A three pole, three position switch 234 controls coil236 of relay CR-l and regulates the function of the two end-of-rollswitches. The first pole disables CR-l in the upper position U todeliver the transistor controlled clutch and brake power to theUpper-roll clutch 182 and brake 184 via contactors 240 and 242respectively. The other brake remains ON. In the Lower position L, thisswitch-pole holds relay CR-l ON, delivering the controlled power to theLower-roll clutch 182 and brake 184, and holding the Upper-roll brake184 ON. In Automatic position A, this pole permits relay CR-l to beenergized by a wide master or original actuating the wide sense switch236. When this happens relay CR-l holes itself until a knife cut dropsits coil 236 voltage, or until coil 236 current is interrupted by themanual roll selector switch 234.

The end-of-roll switches 168 and 170 which are actuated by the absenceof paper in the feed loop position, energize andhold coil 244 of relayCR-2 in the feed-off and brake-on position by closure of contactor 248.The Manual Roll Selector switch 234 disables the opposite end-of-rollcircuit, so that the machine may be used with a single roll.

Brakes 184 are applied byrelay CR-2 so that the operator may turn theR011 Feed OFF and back out a short roll-end. This avoids a-possible jam.If the roll-end paper is sufficiently long to reach the drive roll whichfollows the knife (about 6 inches) it will pass through and cause notrouble.

Jog Switches Upper and Lower-Roll-Jog switches and 152 are provided forloading and testing upper and lower roll drives. The Manual Roll switch234.must be set to the roll used if the other is empty. The ManualCut'switch 154 will finish the JOG feed. Sufiicient (6 inches or more)paper should be fed to avoid a jam build up. I

The power supply for the control circuit of FIG. 4 is provided by atransformer 400 having a secondary winding 401 the center of which isconnected to ground G by a circuit 403 containing a switch 405 which ismechanically connected to a switch 407. The switch 407 connects anothersecondary winding 409 of transformer 400 to a bridge type rectifier 409.Rectifiers 411 are also provided in the ungrounded output circuits 413which are connected to the brake solenoids 184. The bridge 409 suppliesD.C. energy to the clutches 182, knife solenoid 186, and the loopclutches 226.

Referring to FIG. 5, the lamp 28 in the light cylinder 26, FIG. 1,around which the copy paper and original under belts 24 for exposure,shines through a window 500 in an inclined wall in front of the cylinderand into a light tunnel 502, FIG. 5, wherein such light is redirected bya mirror 504 toward a photo-cell 506 located in a housing 508 having anopen top. The photo-cell 506 is connected to a solid state controlcircuit-5l0 which is supplied with energy from a source 512 of DC, anddrives motor 514 at a speed which is governed by the density of eachoriginal moving along path 16 prior to merger withthe correspondingcopy. The motor 514 drives belts 24, FIG. 1, and thus, the speed ofprinting of the apparatus is controlled by the density of each original,producing an exact copy in each case. The greater the original densitythe slower the speed of printing, and vice-versa.

The machine can be operated with only one paper supply roll, or tworolls of equal width, if desired.

What is claimed is:

l. A Diazo printing apparatus comprising in combination means forautomatically drawing copy paper from a selected supply roll of aplurality thereof in response to the feeding of an original into theapparatus, said means including a paper metering roller, means acting tocut such paper so that the length thereof corresponds to that of suchoriginal as they merge for copying, a braking means to brake said copypaper drawing means during the operation of said cutting means, anarmature fixed to one end of said roller, a coil floating on said rollerend, an arm extending radially from said coil, a pair of arm movementlimiting posts located in the path of movement of said arm, controlmeans for energizing said coil shortly prior to the energization of saidpaper cutting means, a spring urging said arm toward one post when saidbrake is released, whereby when said brake is subsequently released saidspring draws said arm back to said post, thereby also turning themetering roll and paper thereon backwardly a short way to prevent thesubsequent cutting of an unwanted sliver therefrom.

2. A Diazo printing machine, as defined in claim 1, wherein said meansfor drawing copy paper from a supply roll in response to the movement ofsuch original toward such line of merger comprises spaced paper feedingrolls between which an elevated loop of the copy paper is normallymaintained, a control switch arm normally resting on such loop, controlcircuit means for operating the leading paper feed roll for feedingpaper only when said switch arm falls with such loop below a preselectedlevel, and stopping such operation when the loop reaches its normallevel, and switch means responsive to such movement of the original foroperating the other paper feed roll to feed copy paper from such looptoward such line of merger with the original, I whereby the copy paperis fed toward such line with substantially little tension.

1. A Diazo printing apparatus comprising in combination means forautomatically drawing copy paper from a selected supply roll of aplurality thereof in response to the feeding of an original into theapparatus, said means including a paper metering roller, means acting tocut such paper so that the length thereof corresponds to that of suchoriginal as they merge for copying, a braking means to brake said copypaper drawing means during the operation of said cutting means, anarmature fixed to one end of said roller, a coil floating on said rollerend, an arm extending radially from said coil, a pair of arm movementlimiting posts located in the path of movement of said arm, controlmeans for energizing said coil shortly prior to the energization of saidpaper cutting means, a spring urging said arm toward one post when saidbrake is released, whereby when said brake is subsequently released saidspring draws said arm back to said post, thereby also turning themetering roll and paper thereon backwardly a short way to prevent thesubsequent cutting of an unwanted sliver therefrom.
 2. A Diazo printingmachine, as defined in claim 1, wherein said means for drawing copypaper from a supply roll in response to the movement of such originaltoward such line of merger comprises spaced paper feeding rolls betweenwhich an elevated loop of the copy paper is normally maintained, acontrol switch arm normally resting on such loop, control circuit meansfor operating the leading paper feed roll for feeding paper only whensaid switch arm falls with such loop below a preselected level, andstopping such operation when the loop reaches its normal level, andswitch means responsive to such movement of the original for operatingthe other paper feed roll to feed copy paper from such loop toward suchline of merger with the original, whereby the copy paper is fed towardsuch line with substantially little tension.